The evolution of wireless communication to fifth generation (5G) standards and technologies provides higher data rates and greater capacity, with improved reliability and lower latency, which enhances mobile broadband services. 5G technologies also provide new classes of services for vehicular, fixed wireless broadband, and the Internet of Things (IoT).
A unified air interface, which utilizes licensed, unlicensed, and shared license radio spectrum, in multiple frequency bands, is one aspect of enabling the capabilities of 5G systems. The 5G air interface utilizes radio spectrum in bands below 1 GHz (sub-gigahertz), below 6 GHz (sub-6 GHz), and above 6 GHz. Radio spectrum above 6 GHz includes millimeter wave (mmWave) frequency bands that provide wide channel bandwidths to support higher data rates for wireless broadband.
To increase the capacity of 5G radio networks, Multiple Input Multiple Output (MIMO) antenna systems support beamformed signals transmitted between base stations and user equipment (UE). In 5G networks, base stations employ a large number of MIMO antennas (e.g., hundreds of antennas) for beamforming signals, which is often referred to as Massive MIMO, to provide beamformed transmission and reception that is focused on small areas of space around individual UE. Massive MIMO beamforming improves network throughput, energy efficiency, and interference rejection. Massive MIMO systems use a channel estimate of the radio frequency (RF) channel characteristics between the base station and the user equipment to determine beamforming coefficients for transmission and reception.
The specification of the features in the 5G air interface for user equipment is defined as 5G New Radio (5G NR). Improvements in beamforming for 5G NR are particularly important at mmWave frequencies where changing channel conditions make it challenging for the UE and a base station to track a beam between the UE and the base station. Synchronization of the beamforming between the UE and the base station in 5G NR is based on broadcast synchronization using cell-specific reference signals that are transmitted periodically by a base station, or the base station may periodically sweep across a set of beams so that the UE can track the base station. Dependence on the periodic broadcasts from a base station limits how quickly the UE can react to changing channel conditions to maintain a communication link with the base station.